Cranberry Health Claims: A Thanksgiving Turkey?

“Research shows benefits of cranberries” proclaimed an Associated Press headline this week – a gentle nudge, I suppose, just in case you forgot to make cranberries part of your Thanksgiving dinner.

But what’s the truth? Does research really “show” that cranberries provide health benefits?

It is a commonly-held notion -- including by many physicians -- that cranberry juice can either prevent and/or treat urinary tract infections, particularly in women. The AP article catered to this belief by stating, “Drinking cranberry juice can block urinary infections by binding to bacteria so they can’t adhere to cell walls.”

To the casual reader, the AP statement appears to reaffirm the conventional wisdom about the benefits of cranberry juice. But in reality, the AP statement seems more misleading than reaffirming.

A recent clinical trial, published in the World Journal of Urology (Feb 2006), certainly did conclude that “cranberry juice consumption provides significant anti-adherence activity against different E.coli uropathogenic strains in the urine compared with placebo.” But there’s more to the study than the face value of the researchers’ conclusion.

The study subjects in the clinical trial consumed up to three 8-ounce servings of either cranberry juice or a placebo at dinner. The following morning their urine was collected and then used as a medium in which to grow bacteria in Petri dishes. The researchers reported a “dose-dependent significant decrease in bacterial adherence associated with cranberry consumption.”

While that’s sounds like an important result, it’s critical to remember that it’s only a laboratory result, the relevance of which to humans is far from clear. The clinical trial did not study whether cranberry juice consumption prevented or treated actual urinary tract infections.

An April 2004 study reviewed seven clinical trials that attempted to examine whether cranberry juice/products prevented urinary tract infections in susceptible populations of men, women and children. The review concluded that there was no evidence that cranberries had any preventative effect in men or children, while two of the trials reported statistically weak preventative effects in women. But the reviewers concluded that neither trial provided evidence concerning the amount and concentration of cranberry juice that needed to be consumed or the length of time for the treatment to be most effective.

With respect to the treatment of urinary tract infections with cranberry juice, a 2000 review by the same researchers reported, “there is no good quality evidence to suggest that [cranberries are] effective for the treatment of urinary tract infections.

The AP article went on to tout cranberries as preventing plaque formation on teeth, killing the H. pylori bacteria that can cause stomach cancer and ulcers. Preliminary research was also touted as showing that drinking cranberry juice daily may raise “good” cholesterol levels, while lowering “bad” cholesterol levels; cranberries may prevent tumors from growing rapidly or starting in the first place; and that cranberry extracts have prevented breast cancer cells from multiplying in a test tube.

But as is the case with cranberries and urinary tract infections, the science is hardly conclusive.

Similar to the situation with urinary tract infections, laboratory research indicates that a compound in cranberries indeed appears to reduce the ability of oral bacteria to adhere to teeth, which has been hypothesized as possibly inhibiting the formation of plaque. But as yet there are no published clinical trials reporting reduced plaque formation in real people who consumed cranberries.

H. pylori is another bacteria hypothesized to be susceptible to cranberries. There is even a clinical trial published in the April 2005 issue of Heliobacter reporting that cranberry juice was associated with suppression of H. pylori.

However, the study was small (200 study subjects), the results were even smaller (14 cranberry juice consumers versus 5 placebo consumers reportedly experienced a significant decrease in H. pylori); and the study was conducted in a region of China that is a high-risk area for stomach cancer, possibly due to dietary factors including low vitamin C intake – which cranberries provide.

Cranberries and cholesterol? I found one recent study (British Journal of Nutrition, August 2006) correlating cranberry juice consumption by abdominally obese men with increased levels of “good” cholesterol. But the study reported no change in levels of “bad” cholesterol. Another study of female cranberry juice drinkers (European Journal of Nutrition, March 2006) reported that cranberry juice had no effect on either “good” or “bad” cholesterol levels.

As to cranberry consumption preventing or inhibiting the rate of tumor growth – another idea out of the laboratory as opposed to real-world human populations – the European Journal of Nutrition study reported that cranberry consumption had no effect on basal or induced oxidative DNA damage” – a biological mechanism for carcinogenesis.

The researchers wryly concluded, “These results show the importance of distinguishing between the in vitro [laboratory] and in vivo [real-world] antioxidant activities of dietary [cranberries] in relation to human health.

Let’s consume cranberry products and dishes because they’re tasty – not because they’ve been prematurely proclaimed as being a dietary magic bullet that will prevent cancer, heart disease, ulcers, urinary tract infections and, of course, dreaded dental plaque. Unlike the science, taste is something that cranberries actually have going for them.